Method for manufacturing an electrical bushing for an implantable medical device

ABSTRACT

One aspect relates to an electrical bushing for use in a housing of an implantable medical device. The electrical bushing includes at least one electrically insulating base body and at least one electrical conducting element. The electrical bushing includes a holding element to hold the electrical bushing in or on the housing. The conducting element is set-up to establish, through the base body, at least one electrically conductive connection between an internal space of the housing and an external space. The conducting element is hermetically sealed with respect to the base body. The at least one conducting element includes at least one cermet. The holding element is made, to at least 80% by weight with respect to the holding element, from a material selected from the group consisting of a metal from any of the subgroups IV, V, VI, VIII, IX, and X of the periodic system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Non-Provisional Patent Application claims the benefit of the filingdate of U.S. Provisional Patent Application Ser. No. 61/438,063, filedJan. 31, 2011, entitled “CERMET-CONTAINING BUSHING WITH HOLDING ELEMENTFOR AN IMPLANTABLE MEDICAL DEVICE,” and this Patent Application alsoclaims priority to German Patent Application No. DE 10 2011 009 862.3,filed on Jan. 31, 2011, and both of which are incorporated herein byreference.

This Patent Application is also related to patent application Ser. No.13/361,322 filed on Jan. 30, 2012, entitled “CERAMIC BUSHING FOR ANIMPLANTABLE MEDICAL DEVICE”; patent application Ser. No. 13/361,340filed on Jan. 30, 2012, entitled “DIRECTLY APPLICABLE ELECTRICALBUSHING”; patent application Ser. No. 13/361,348 filed on Jan. 30, 2012,entitled “IMPLANTABLE DEVICE HAVING AN INTEGRATED CERAMIC BUSHING”;patent application Ser. No. 13/361,355 filed on Jan. 30, 2012, entitled“HEAD PART FOR AN IMPLANTABLE MEDICAL DEVICE”; patent application Ser.No. 13/361,362 filed on Jan. 30, 2012, entitled “CERMET-CONTAININGBUSHING FOR AN IMPLANTABLE MEDICAL DEVICE HAVING A CONNECTING LAYER”;patent application Ser. No. 13/361,370 filed on Jan. 30, 2012, entitled“ELECTRICAL BUSHING WITH CERMET-CONTAINING CONNECTING ELEMENT FOR ANACTIVE IMPLANTABLE MEDICAL DEVICE”; patent application Ser. No.13/361,374 filed on Jan. 30, 2012, entitled “CERAMIC BUSHING WITHFILTER”; patent application Ser. No. 13/361,383 filed on Jan. 30, 2012,entitled “CERAMIC BUSHING WITH INDUCTIVE FILTER”; patent applicationSer. No. 13/361,388 filed on Jan. 30, 2012, entitled “CERAMIC BUSHINGHAVING HIGH CONDUCTIVITY CONDUCTING ELEMENTS”; patent application Ser.No. 13/361,398 filed on Jan. 30, 2012, entitled “METHOD FOR THEMANUFACTURE OF A CERMET-CONTAINING BUSHING”; and patent application Ser.No. 13/361,404 filed on Jan. 30, 2012, entitled “METHOD FOR THEMANUFACTURE OF A CERMET-CONTAINING BUSHING FOR AN IMPLANTABLE MEDICALDEVICE”.

BACKGROUND

One aspect relates to an electrical bushing for use in a housing of animplantable medical device. Moreover, one aspect relates to a method forthe manufacture of an electrical bushing for an implantable medicaldevice.

The post-published document, DE 10 2009 035 972, discloses an electricalbushing for an implantable medical device having the features of thepreamble of claim 1. Moreover, a use of at least one cermet-comprisingconducting element in an electrical bushing for an implantable medicaldevice and a method for the manufacture of an electrical bushing for animplantable medical device are disclosed.

A multitude of electrical bushings for various applications are known,examples including: U.S. Pat. Nos. 4,678,868, 7,564,674 B2, US2008/0119906 A1, U.S. Pat. Nos. 7,145,076 B2, 7,561,917, US 2007/0183118A1, U.S. Pat. Nos. 7,260,434B1, 7,761,165, U.S. Pat. Nos. 7,742,817 B2,7,736,191 B1, US 2006/0259093 A1, U.S. Pat. No. 7,274,963 B2, US2004116976 A1, U.S. Pat. No. 7,794,256, US 2010/0023086 A1, U.S. Pat.Nos. 7,502,217 B2, 7,706,124 B2, 6,999,818 B2, EP 1754511 A2, U.S. Pat.No. 7,035,076, EP 1685874 A1, WO 03/073450 A1, U.S. Pat. Nos. 7,136,273,7,765,005, WO 2008/103166 A1, US 2008/0269831, U.S. Pat. No. 7,174,219B2, WO 2004/110555 A1, U.S. Pat. No. 7,720,538 B2, WO 2010/091435, US2010/0258342 A1, US 2001/0013756 A1, U.S. Pat. No. 4,315,054, and EP0877400.

DE 697 297 19 T2 describes an electrical bushing for an activeimplantable medical device—also called implantable device or therapeuticdevice. Electrical bushings of this type serve to establish electricalconnection between a hermetically sealed interior and an exterior of thetherapeutic device. Known implantable therapeutic devices are cardiacpacemakers or defibrillators, which usually include a hermeticallysealed metal housing which is provided with a connection body, alsocalled header, on one side. Said connection body includes a hollow spacehaving at least one connection socket that serves for connectingelectrode leads. In this context, the connection socket includeselectrical contacts in order to electrically connect electrode leads tothe control electronics on the interior of the housing of theimplantable therapeutic device. Hermetic sealing with respect to asurrounding is an essential prerequisite of an electrical bushing ofthis type. Therefore, lead wires that are introduced into anelectrically insulating base body—also called signal-transmissionelements—through which the electrical signals are propagated, must beintroduced into the base body such as to be free of gaps. In thiscontext, it has proven to be challenging that the lead wires generallyare made of a metal and are introduced into a ceramic base body. Inorder to ensure durable connection between the two elements, theinternal surface of a through-opening—also called openings—in the basebody is metallized in order to attach the lead wires by soldering.However, the metallization has proven to be difficult to apply in thethrough-opening. Only cost-intensive procedures ensure homogeneousmetallization of the internal surface of the bore hole—and thus ahermetically sealed connection of the lead wires to the base body bysoldering. The soldering process itself requires additional components,such as solder rings. Moreover, the process of connecting the lead wiresto the previously metallized insulators utilizing the solder rings is aprocess that is laborious and difficult to automate.

For these and other reasons there is a need for the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofembodiments will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Furthermeasures and advantages of the invention are evident from the claims,the description provided hereinafter, and the drawings. The invention isillustrated through several exemplary embodiments in the drawings. Inthis context, equal or functionally equal or functionally correspondingelements are identified through the same reference numbers. Theinvention shall not be limited to the exemplary embodiments.

FIG. 1 illustrates an implantable medical device.

FIG. 2 illustrates a sectional drawing through an electrical bushingaccording to one embodiment.

FIG. 3 illustrates a schematic top view onto the electrical bushingaccording to FIG. 2.

FIG. 4 illustrates a magnified detail of the electrical bushing.

FIG. 5 illustrates a sketch of the procedural steps involved in themanufacture of an electrical bushing having a holding element.

FIG. 6 illustrates a sketch of a rectangular bushing surrounded by aholding element.

FIG. 7 illustrates a sketch of a T-shaped bushing surrounded by a roundholding element.

FIG. 8 illustrates a sketch of a T-shaped bushing surrounded by holdingelements, having multiple contacted cermet conducting elements,incorporated into a housing of a medical device.

FIG. 9 illustrates a sketch of a bushing having a holding element in afurnace.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of embodiments can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

It is to be understood that the features of the various exemplaryembodiments described herein may be combined with each other, unlessspecifically noted otherwise.

One embodiment creates an electrical bushing for an implantable medicaldevice, in which at least one of the disadvantages mentioned above isprevented at least in part. One embodiment creates a durable connectionof an electrical bushing in or on a housing of a medical device.Features and details that are described in the context of the electricalbushing or the implantable medical device shall also apply in relationto the method, and vice versa.

In summary, the following embodiments are proposed:

An electrical bushing for use in a housing of an implantable medicaldevice, whereby the electrical bushing includes at least oneelectrically insulating base body and at least one electrical conductingelement, whereby the electrical bushing further includes at least oneholding element in order to hold the electrical bushing in or on ahousing, whereby the conducting element is set-up to establish, throughthe base body, at least one electrically conducting connection betweenan internal space of the housing and an external space, whereby theconducting element is hermetically sealed with respect to the base body,whereby the at least one conducting element includes at least onecermet, whereby the holding element in one embodiment consists of atleast 80% by weight, in one embodiment at least 90% by weight, and inone embodiment at least 99% by weight, each with respect to the holdingelement (20), of a material selected from the group consisting of ametal from any of subgroups V, VI, VIII, IX and X of the periodic systemof the elements or at least two of these. The selection of suitablematerials includes all substances and mixtures thereof that are known toa person skilled in the art and are characterized, for example, by highbio-compatibility. Consequently, said materials are to withstand theconditions inside the body, in which the medical device having theelectrical bushing according to one embodiment is inserted, for as longas possible and essentially without being changed. Metals, mixtures andalloys from the above-mentioned subgroups, for example, arepossibilities in this regard. The mixtures and alloys can involve eitherthe metals of the above-mentioned subgroups or mixtures and alloys madefrom one or more of these metals and other metals can be used. Mainly,those mixtures and alloys that are capable of forming a stableconnection to the base body of the electrical bushing are preferred inone embodiment.

In one embodiment, the material is selected from the group consisting ofplatinum (Pt), iron (Fe), iridium (Ir), niobium (Nb), molybdenum (Mo),tungsten (W), titanium (Ti), cobalt (Co), chromium (Cr), for example,cobalt-chromium alloys, and zirconium (Zr) as well as at least two ofthese, with Ti, Nb, Mo, Co, Cr and alloys thereof being. Said metals caneach be used alone or in combination with each other or in combinationwith other materials, such as other metals. For example, alloys made ofniobium and one of the other above-mentioned metals are preferred in oneembodiment. Iron alloys, often referred to as stainless steel, are alsopreferred in one embodiment. Platinum and platinum alloys as well ascobalt-chromium alloys are also preferred in one embodiment.

In an embodiment of the electrical bushing according to one embodiment,the base body and the at least one conducting element are connected in afirmly bonded manner, for example, through a firmly bonded sinteredconnection. The process of sintering shall be illustrated in more detailbelow.

In an embodiment of the electrical bushing according to one embodiment,the base body is made, at least in part, from an insulating compositionof materials.

In an embodiment of the electrical bushing, the insulating compositionof materials is selected from the group consisting of: aluminum oxide,magnesium oxide, zirconium oxide, aluminum titanate and piezoceramicmaterials. Processed into ceramic materials, said materials displayparticularly high thermal resistance, mechanical strength, and inertbehavior with respect to acids and bases. This renders them particularlywell-suited for use as a biocompatible material in implantable medicaldevices.

The proposed electrical bushing is set-up for use in an implantablemedical device, whereby the implantable medical device can be provided,in one embodiment, as an active implantable medical device (AIMD) and inone embodiment as a therapeutic device.

As a matter of principle, the term, implantable medical device, shallinclude any device which is set-up to perform at least one medicalfunction and which can be introduced into a body tissue of a human oranimal user. As a matter of principle, the medical function can includeany function selected from the group consisting of a therapeuticfunction, a diagnostic function, and a surgical function. For example,the medical function can include at least one actuator function, inwhich an actuator is used to exert at least one stimulus on said bodytissue, for example, an electrical stimulus.

As a matter of principle, the term, active implantable medicaldevice—also called AIMD—shall include all implantable medical devicesthat can conduct electrical signals from a hermetically sealed housingto a part of the body tissue of the user and/or receive electricalsignals from the part of the body tissue of the user. Accordingly, theterm, active implantable medical device, includes, for example, cardiacpacemakers, cochlea implants, implantable cardioverters/defibrillators,nerve, brain, organ or muscle stimulators as well as implantablemonitoring devices, hearing aids, retinal implants, muscle stimulators,implantable drug pumps, artificial hearts, bone growth stimulators,prostate implants, stomach implants or the like.

The implantable medical device, for example, the active implantablemedical device, can usually include, for example, at least one housing,for example, at least one hermetically sealed housing. The housing canin one embodiment enclose at least one electronics unit, for example atriggering and/or analytical electronics unit of the implantable medicaldevice.

In the scope of one embodiment, a housing of an implantable medicaldevice shall be understood to be an element that encloses, at least inpart, at least one functional element of the implantable medical devicethat is set up to perform the at least one medical function or promotesthe medical function. For example, the housing includes at least oneinternal space that takes up the functional element fully or in part.For example, the housing can be set up to provide mechanical protectionto the functional element with respect to strains occurring duringoperation and/or upon handling, and/or protection to the functionalelement with respect to influences from its surroundings such as, forexample, influences of a body fluid. The housing can, for example,border and/or close the implantable medical device with respect to theoutside.

In this context, an internal space shall be understood herein to mean aregion of the implantable medical device, for example, within thehousing, which can take up the functional element fully or in part andwhich, in an implanted state, does not contact the body tissue and/or abody fluid. The internal space can include at least one hollow spacewhich can be closed fully or in part. Alternatively, the internal spacecan be filled fully or in part, for example, by the at least onefunctional element and/or by at least one filling material, for exampleat least one casting, for example at least one casting material in theform of an epoxy resin or a similar material.

An external space, in contrast, shall be understood to be a regionoutside of the housing. This can, for example, be a region which, in theimplanted state, can contact the body tissue and/or a body fluid.Alternatively or in addition, the external space can just as well be orinclude a region that is only accessible from outside the housingwithout necessarily contacting the body tissue and/or the body fluid,for example a region of a connecting element of the implantable medicaldevice that is accessible from outside to an electrical connectingelement, for example an electrical plug connector.

The housing and/or, for example, the electrical bushing can, forexample, be provided to be hermetically sealed such that, for example,the internal space, is hermetically sealed with respect to the externalspace. In this context, the term, “hermetically sealed”, can illustratethat moisture and/or gases cannot permeate through the hermeticallysealed element at all or only to a minimal extent upon intended use forthe common periods of time (for example 5-10 years). The leakage rate,which can be determined, for example, by leak tests, is a physicalparameter that can described, for example, a permeation of gases and/ormoisture through a device, for example, through the electrical bushingand/or the housing. Pertinent leak tests can be carried out with heliumleak testers and/or mass spectrometers and are specified in theMil-STD-883G Method 1014 standard. In this context, the maximalpermissible helium leak rate is determined as a function of the internalvolume of the device to be tested. According to the methods specified inMIL-STD-883G, method 1014, section 3.1 and taking into consideration thevolumes and cavities of the devices to be tested that are used in theapplication of one embodiment, said maximal permissible helium leakrates can, for example, be from 1×10⁻⁸ atm*cm³/sec to 1×10⁻⁷atm*cm³/sec. In the scope of one embodiment, the term, “hermeticallysealed”, shall be understood, for example, to mean that the device to betested (for example the housing and/or the electrical bushing and/or thehousing with the electrical bushing) has a helium leak rate of less than1×10⁻⁷ atm*cm³/sec. In one embodiment, the helium leak rate can be lessthan 1×10⁻⁸ atm*cm³/sec, in one embodiment, less than 1×10⁻⁹atm*cm³/sec. For the purpose of standardization, the above-mentionedhelium leak rates can also be converted into the equivalent standard airleak rate. The definition of the equivalent standard air leak rate andthe conversion are specified in the ISO 3530 standard.

Electrical bushings are elements set-up to create at least oneelectrically conducting path that extends between the internal space ofthe housing to at least one external point or region outside thehousing, for example, situated in the external space. Accordingly, thisestablishes an electrical connection to leads, electrodes, and sensorsthat are arranged outside the housing, for example.

Common implantable medical devices are commonly provided with a housing,which can include, on one side, a head part, also called header orconnecting body, that carries connection sockets for connection ofleads, also called electrode leads. The connection sockets include, forexample, electrical contacts that serve to electrically connect theleads to a control electronics unit on the interior of the housing ofthe medical device. Usually, an electrical bushing is provided in thelocation, at which the electrical connection enters into the housing ofthe medical device, and the electrical bushing is inserted into acorresponding opening of the housing in a hermetically sealing manner.

Due to the type of use of implantable medical devices, their hermeticsealing and biocompatibility are usually amongst the foremostrequirements. The implantable medical device proposed herein accordingto one embodiment, can be inserted, for example, into a body of a humanor animal user, for example, of a patient. As a result, the implantablemedical device is usually exposed to a fluid of a body tissue of thebody. Accordingly, it is usually important that no body fluid penetratesinto the implantable medical device and that no liquids leak from theimplantable medical device. In order to ensure this, the housing of theimplantable medical device, and thus the electrical bushing as well,should be as impermeable as possible, for example, with respect to bodyfluids.

Moreover, the electrical bushing should ensure high electricalinsulation between the at least one conducting element and the housingand/or the multiple conducting elements provided that more than oneconducting element are present. In this context, in one embodiment theinsulation resistance reached is at least several MOhm, in oneembodiment, more than 20 MOhm, and the leakage currents reached can besmall, in one embodiment, less than 10 pA. Moreover, in case multipleconducting elements are present, the crosstalk and electromagneticcoupling between the individual conducting elements in one embodimentare below the specified thresholds for medical applications.

The electrical bushing disclosed according to one embodiment isparticularly well-suited for the above-mentioned applications. Moreover,the electrical bushing can also be used in other applications that areassociated with special requirements with regard to biocompatibility,tight sealing, and stability.

The electrical bushing according to one embodiment can meet, forexample, the above-mentioned tight sealing requirements and/or theabove-mentioned insulation requirements.

As mentioned above, the electrical bushing includes at least oneelectrically insulating base body. In the scope of one embodiment, abase body shall be understood to mean an element that serves amechanical holding function in the electrical bushing, for example inthat the base body holds or carries the at least one conducting elementeither directly or indirectly. For example, the at least one conductingelement can be embedded in the base body directly or indirectly, fullyor partly, for example, through a firmly bonded connection between thebase body and the conducting element and for example, throughco-sintering the base body and the conducting element. For example, thebase body can have at least one side facing the internal space and atleast one side facing the external space and/or accessible from theexternal space.

As mentioned above, the base body is provided to be electricallyinsulating. This means that the base body, fully or at least regionsthereof, is made of at least one electrically insulating material. Inthis context, an electrically insulating material shall be understood tomean a material with a resistivity of at least 10⁷ Ohm*m, in oneembodiment, of at least 10⁸ Ohm*m, in one embodiment of at least 10⁹Ohm*m, and in one embodiment of at least 10¹¹ Ohm*m. For example, thebase body can be provided such that, as mentioned above, a flow ofcurrent between the conducting element and the housing and/or betweenmultiple conducting elements is at least largely prevented, for examplethrough the resistivity values between the conducting element and thehousing as specified above being implemented. For example, the base bodycan include at least one ceramic material.

In this context, a conducting element or electrical conducting elementshall generally be understood to mean an element set-up to establish anelectrical connection between at least two sites and/or at least twoelements. For example, the conducting element can include one or moreelectrical conductors, for example metallic conductors. In the scope ofone embodiment, the conducting element is made fully or partly of atleast one cermet, as mentioned above. In addition, one or more otherelectrical conductors, for example metallic conductors, can be provided.The conducting element can, for example, be provided in the form of oneor more contact pins and/or curved conductors. Moreover, the conductingelement can include, for example, on a side of the base body and/orelectrical bushing facing the internal space or on a side of the basebody and/or electrical bushing facing the external space or accessiblefrom the external space, one or more connecting contacts, for exampleone or more plug-in connectors, for example one or more connectingcontacts, which project from the base body or can be electricallycontacted through other means from the internal space and/or theexternal space.

The at least one conducting element can establish the electricallyconducting connection between the internal space and the external spacein a variety of ways. For example, the conducting element can extendfrom at least one section of the conducting element that is arranged onthe side of the base body facing the internal space to at least onesection of the conducting element arranged on the side facing theexternal space or accessible from the external space. However, otherarrangements are also feasible as a matter of principle. Accordingly,the conducting element can just as well include a plurality of partialconducting elements that are connected to each other in an electricallyconducting manner. Moreover, the conducting element can extend into theinternal space and/or the external space. For example, the conductingelement can include at least one region that is arranged in the internalspace and/or at least one region that is arranged in the external space,whereby the regions can, for example, be electrically connected to eachother. Various exemplary embodiments shall be illustrated in more detailbelow.

The at least one conducting element can include, on a side of the basebody and/or electrical bushing facing the internal space or on a side ofthe base body and/or electrical bushing facing the external space oraccessible from the external space, at least one electrical connectingelement and/or be connected to an electrical connecting element of thistype. For example, as described above, one or more plug-in connectorsand/or one or more contact surfaces and/or one or more contact springsand/or one or more types of electrical connecting elements can beprovided on one or both of said sides. The at least one optionalconnecting element can, for example, be a component of the at least oneconducting element and/or can be connected to the at least oneconducting element in an electrically conducting manner. For example,one or more conducting elements of the bushing can be contacted to oneor more internal connecting elements and/or one or more externalconnecting elements. The material of the internal connecting elementsshould be suited for permanent connection to the conducting element. Theexternal connecting elements should be biocompatible and should be suchthat they can be permanently connected to the at least one conductingelement.

The electrically insulating base body can support, as a bearing, forexample, the at least one conducting element. The at least one materialof the base body should be biocompatible in one embodiment, as mentionedabove, and should have sufficiently high insulation resistance. It hasproven to be advantageous in one embodiment for the base body to includeone or more materials selected from the group consisting of: aluminumoxide (Al₂O₃), zirconium dioxide (ZrO₂), aluminum oxide-toughenedzirconium oxide (ZTA), zirconium oxide-toughened aluminum oxide(ZTA—Zirconia Toughened Aluminum—Al₂O₃/ZrO₂), yttrium-toughenedzirconium oxide (Y-TZP), aluminum nitride (AlN), magnesium oxide (MgO),piezoceramic materials, barium(Zr, Ti) oxide, barium(CE, Ti) oxide, andsodium-potassium-niobate.

The holding element includes the base body and serves as connectingelement to the housing of the implantable device. The materials of theholding element should be biocompatible, easy to process,corrosion-resistant, and permanently connectable to the base body andthe housing in a firmly bonded manner. It has proven to be advantageousfor the holding element according to one embodiment to include at leastone of the following metals and/or an alloy based on at least one of thefollowing metals: platinum, iridium, niobium, molybdenum, tantalum,tungsten, titanium, cobalt-chromium alloys or zirconium.

In the proposed electrical bushing, the at least one conducting elementincludes at least one cermet.

The base body can, for example, be made fully or partly from one or moresinterable materials, for example, from one or more ceramic-basedsinterable materials. The conducting element or elements can fully orpartly be made of one or more cermet-based sinterable materials.Moreover, the at least one conducting element can also, as mentionedabove, include one or more additional conductors, for example one ormore metallic conductors.

In the scope of one embodiment, “cermet” shall refer to a compositematerial made of one or more ceramic materials in at least one metallicmatrix or a composite material made of one or more metallic materials inat least one ceramic matrix. For production of a cermet, for example, amixture of at least one ceramic powder and at least one metallic powdercan be used to which, for example, at least one binding agent and, ifapplicable, at least one solvent can be added.

In the scope of one embodiment, sintering or a sintering process shallgenerally be understood to mean a method for producing materials orwork-pieces, in which powdered, for example, fine-grained, ceramicand/or metallic substances are heated and thus connected. This processcan proceed without applying external pressure onto the substance to beheated or can, for example, proceed under elevated pressure onto thesubstance to be heated, for example under a pressure of at least 2 bar,in one embodiment higher pressures, for example pressures of at least 10bar, in one embodiment, at least 100 bar, or even at least 1000 bar. Theprocess can proceed, for example, fully, or partly at temperatures belowthe melting temperature of the powdered materials, for example attemperatures of 700° C. to 1400° C. The process can be implemented, forexample, fully, or partly in a tool and/or a mold such that a formingstep can be associated with the sintering process. Aside from thepowdered materials, a starting material for the sintering process caninclude further materials, for example one or more binding agents and/orone or more solvents. The sintering process can proceed in one or moresteps, whereby additional steps can precede the sintering process, forexample one or more forming steps and/or one or more debinding steps.

Producing the at least one conducting element and/or optionallyproducing the at least one base body, a method can be used for example,in which at least one green compact is produced first, subsequently atleast one brown compact is produced from said green compact, andsubsequently the finished work-piece is produced from said brown compactthrough at least one sintering step. In this context, separate greencompacts and/or separate brown compacts can be produced for theconducting element and the base body and can be connected subsequently.Alternatively, one or more common green compacts and/or brown compactscan be produced for the base body and the conducting element.Alternatively again, separate green compacts can be produced first, saidgreen compacts can then be connected, and subsequently a common browncompact can be produced from the connected green compact. In general, agreen compact shall be understood to mean a pre-form body of awork-piece which includes the starting material, for example the atleast one ceramic and/or metallic powder, as well as, if applicable, theone or more binding agents and/or one or more solvents. A brown compactshall be understood to mean a pre-form body which is generated from thegreen compact through at least one debinding step, for example at leastone thermal and/or chemical debinding step, whereby the at least onebinding agent and/or the at least one solvent is removed, at leastpartly, from the pre-form body in the debinding step.

The sintering process, for example, of a cermet, but of the base bodyjust as well, for example, can proceed comparable to a sintering processthat is commonly used for homogeneous powders. For example, the materialcan be compacted in the sintering process at high temperature and, ifapplicable, high pressure such that the cermet is virtually sealed tightor has no more than closed porosity. Usually, cermets are characterizedby their particularly high toughness and wear resistance. Compared tosintered hard metals, a cermet-containing transmission element usuallyhas a higher thermal shock and oxidation resistance and usually athermal expansion coefficient that is matched to a surroundinginsulator.

For the bushing according to one embodiment, the at least one ceramiccomponent of the cermet can include, for example, at least one of thefollowing materials: aluminum oxide (Al₂O₃), zirconium dioxide (ZrO₂),aluminum oxide-toughened zirconium oxide (ZTA), zirconiumoxide-toughened aluminum oxide (ZTA—Zirconia ToughenedAluminum—Al₂O₃/ZrO₂), yttrium-toughened zirconium oxide (Y-TZP),aluminum nitride (AlN), magnesium oxide (MgO), piezoceramic materials,barium(Zr, Ti) oxide, barium(CE, Ti) oxide, or sodium-potassium-niobate.

For the bushing according to one embodiment, the at least one metalliccomponent of the cermet can include, for example, at least one of thefollowing metals and/or an alloy based on at least one of the followingmetals: platinum, iridium, niobium, molybdenum, tantalum, tungsten,titanium, cobalt or zirconium. An electrically conductive connection isusually established in the cermet when the metal content exceeds theso-called percolation threshold at which the metal particles in thesintered cermet are connected to each other, at least in spots, suchthat electrical conduction is enabled. For this purpose, experiencetells that the metal content should be 25% by volume and more, in oneembodiment 32% by volume, in one embodiment, more than 38% by volume,depending on the selection of materials.

In the scope of one embodiment, the terms, “including a cermet,”“cermet-including,” “comprising a cermet,” and “cermet-containing”, areused synonymously. Accordingly, the terms refer to the property of anelement, being that the element contains cermet. This meaning alsoincludes the variant of an embodiment in that elements, for example theconducting element, consist of a cermet, that is, are fully made of acermet.

In one embodiment, both the at least one conducting element and the basebody can include one or more components which are or can be produced ina sintering procedure, or the at least one conducting element and thebase body are or can both be produced in a sintering procedure. Forexample, the base body and the conducting element are or can be producedin a co-sintering procedure, that is, a procedure of simultaneoussintering of these elements. For example, the conducting element and thebase body each can include one or more ceramic components that areproduced, and in one embodiment compacted, in the scope of at least onesintering procedure.

For example, a base body green compact can be produced from aninsulating composition of materials. This can proceed, for example, bycompressing the composition of materials in a mold. In this context, theinsulating composition of materials in one embodiment is a powder mass,in which the powder particles illustrate at least minimal cohesion. Inthis context, the production of a green compact proceeds, for example,through compressing powder masses or through forming followed by drying.

Said procedural steps can also be utilized to form at least onecermet-containing conducting element green compact. In this context, oneembodiment can provide that the powder, which is compressed into theconducting element green compact, is cermet-containing or consists of acermet or includes at least one starting material for a cermet.Subsequently, the two green compacts—the base body green compact and theconducting element green compact—can be combined. The production of theconducting element green compact and the base body green compact canjust as well proceed simultaneously, for example, by multi-componentinjection molding, co-extrusion, etc., such that there is no longer aneed to connect them subsequently.

While the green compacts are being sintered, they are in one embodimentsubjected to a heat treatment below the melting temperature of thepowder particles of the green compact. This usually leads to compactionof the material and ensuing substantial reduction of the porosity andvolume of the green compacts. Accordingly, in one embodiment of themethod the base body and the conducting element can be sintered jointly.Accordingly, there is in one embodiment no longer a need to connect thetwo elements subsequently.

Through the sintering, the conducting element becomes connected to thebase body in one embodiment in a positive fit-type and/or non-positivefit-type and/or firmly bonded manner. In one embodiment, this achieveshermetic integration of the conducting element into the base body. Inone embodiment, there is no longer a need for subsequent soldering orwelding of the conducting element into the base body. Rather, ahermetically sealing connection between the base body and the conductingelement is attained through the joint sintering in one embodiment andutilization of a cermet-containing green compact in one embodiment.

One refinement of the method is characterized in that the sinteringincludes only partial sintering of the at least one optional base bodygreen compact, whereby said partial sintering can effect and/or include,for example, the debinding step mentioned above. The green compact is inone embodiment heat-treated in the scope of said partial sintering. Thisis usually already associated with some shrinkage of the volume of thegreen compact. However, the volume of the green compact has not yetreached its final state. Rather, another heat treatment is usuallyneeded—a final sintering—in which the green compact(s) is/are shrunk totheir final size. In the scope of said variant of an embodiment, thegreen compact is in one embodiment sintered only partly in order toattain some stability to render the green compact easier to handle.

The starting material used for producing at least one conducting elementgreen compact and/or at least one base body green compact can, forexample, be a dry powder or include a dry powder, whereby the dry powderis compressed in the dry state into a green compact and illustratessufficient adhesion to maintain its compressed green compact shape.However, optionally, the starting material can include one or morefurther components in addition to the at least one powder, for example,as mentioned above, one or more binding agents and/or one or moresolvents. Said binding agents and/or solvents, for example organicand/or inorganic binding agents and/or solvents, are generally known tothe person skilled in the art, and are commercially available. Thestarting material can, for example, include one or more slurries or be aslurry. In the scope of one embodiment, a slurry is a suspension ofparticles of a powder made of one or more materials in a liquid bindingagent, and, if applicable, in a water-based or organic binding agent. Aslurry has a high viscosity and can easily be shaped into a greencompact without the application of high pressure.

In the case of green compacts made from slurries, the sintering process,which is generally carried out below the melting temperature of theceramic, cermet or metal materials that are used, but in individualcases can also be carried out just above the melting temperature of thelower melting component of a multi-component mixture, this usually beingthe metal component, leads to the binding agent slowly diffusing fromthe slurry. Overly rapid heating leads to a rapid increase of the volumeof the binding agent by transition to the gas phase and destruction ofthe green compact or formation of undesired defects in the work-piece.

Thermoplastic and duroplastic polymers, waxes, thermogelling substancesand/or surface-active substances, for example, can be used as bindingagent—also called binder. In this context, these can be used alone or asbinding agent mixtures of multiple components of this type. Ifindividual elements or all elements of the bushing (base body greencompact, conducting element green compact, bushing blank) are producedin the scope of an extrusion procedure, the composition of the bindingagent should be such that the line of the elements extruded through thenozzle is sufficiently stable in shape for the shape defined by thenozzle to easily be maintained. Suitable binders, also called bindingagents, are known to the person skilled in the art.

In contrast, the conducting element according to the prior art usuallyis a metal wire. A conducting element provided with a cermet, as is inaccordance with one embodiment, can be connected easily to the base bodysince it is a ceramic material. Accordingly, green compacts of both theconducting element and the base body can be produced and subsequentlysubjected to a sintering process. The resulting electrical bushing isnot only biocompatible and durable, but also possesses good hermeticsealing properties. Thus, no fissures or connecting sites still to besoldered result between the conducting element and the base body.Rather, sintering results in the base body and the conducting elementbecoming connected. A variant of an embodiment therefore provides the atleast one conducting element to consist of a cermet. In this variant ofan embodiment, the conducting element includes not only components madeof cermet, but is fully made of a cermet.

Generally, cermets are characterized by their particularly hightoughness and wear resistance. The “cermets” and/or “cermet-containing”substances can, for example, be or include cutting materials related tohard metals which can dispense with tungsten carbide as the hardsubstance and can be produced, for example, by a powder metallurgicalroute. A sintering process for cermets and/or the cermet-containingconducting element proceeds, for example, alike a process forhomogeneous powders except that, at identical compression force, themetal is usually compacted more strongly than the ceramic material.Compared to sintered hard metals, the cermet-containing conductingelement usually illustrates higher resistance to thermal shock andoxidation.

As mentioned above, the ceramic components, for example, in the basebody, can be, in one embodiment, aluminum oxide (Al₂O₃) and/or zirconiumdioxide (ZrO₂), whereas in one embodiment, niobium, molybdenum,titanium, cobalt, zirconium, chromium are conceivable as metalliccomponents, which are in one embodiment used in the holding element. Inone embodiment, the ceramic component, Al₂O₃, in combination withniobium, iron, platinum or molybdenum is preferred. The ceramiccomponent, ZrO₂, combined with niobium as metallic component is analternative. The preceding combinations are particularly well-suited forthe connecting according to one embodiment, which is often referred toas “diffusion-bonding”.

For integration of the electrical bushing in the housing of a cardiacpacemaker, the electrical bushing includes a holding element. In oneembodiment, said holding element is arranged to be situated around anentire surface of the base body. Depending on the shape of the basebody, the holding element is arranged around the base body, for example,in an annular or ring shape. The purpose of the holding element is toestablish a non-positive fit- and/or positive fit-type connection of thebase body to the housing. A hermetically sealed connection between theholding element and the housing is to be formed in the process. In oneembodiment, the holding element includes a composition of materials, inwhich the metal oxide fraction, such as of aluminum oxide (Al₂O₃),magnesium oxide (MgO), zirconium oxide (ZrO₂), aluminum titanate(Al₂TiO₅), and piezoceramic materials, is less than 20% by weight withrespect to the holding element. In one embodiment, the fraction of metaloxides is less than 10% by weight and in one embodiment is less than 1%by weight, each with respect to the holding element. In one embodiment,the electrical bushing includes a holding element that does not includea cermet. The effect of the low metal oxide fraction is that the holdingelement is not only easy to manufacture and to connect to the electricalbushing, but also is more flexible in use than a holding element with ametal oxide fraction that is too high. The higher the metal oxidefraction, the less deformable is the holding element, which can lead tothe handling of the holding element becoming more inflexible. Moreover,the holding element is particularly flexible in use if it can also beconnected easily to other materials, such as, for example, a housing ofa device. This is more likely to be provided by the holding elementhaving a high metal content, as proposed according to one embodiment,than with a cermet or a ceramic material.

The metal-containing holding element can be connected to the housing ofthe implantable medical device in an easy, durable and hermeticallysealed manner. Since both the holding element and the conducting elementare still to be connected to metallic components, both should includemeans to be welded or soldered to them. In an embodiment according toone embodiment, the holding element consists, at least in part, of amaterial selected from the group consisting of platinum (Pt), iron (Fe),iridium (Ir), niobium (Nb), molybdenum (Mo), tungsten (W), titanium(Ti), cobalt (Co), chromium (Cr), for example, cobalt-chromium alloys,and zirconium (Zr) as well as at least two of these or alloys thatinclude other metals.

One embodiment includes a base body that is formed from an insulatingcomposition of materials. The purpose of the base body is to insulatethe conducting wire from the holding element and the other objects ofthe implantable medical device. Electrical signals that are propagatedthrough the conducting wire shall not be attenuated or short-circuitedby contacting the housing of the implantable device. In addition, thecomposition of the base body must be biocompatible for implantation inmedical applications. For this reason, it is preferred in one embodimentthat the base body consists of a glass-ceramic or glass-like material.It has been found to be preferred in one embodiment that the insulatingcomposition of materials of the base body is at least any one from thegroup, aluminum oxide (Al₂O₃), magnesium oxide (MgO), zirconium oxide(ZrO₂), aluminum titanate (Al₂TiO₅), and piezoceramic materials. In thiscontext, aluminum oxide features high electrical resistance and lowdielectric losses. These properties are supplemented by the additionalhigh thermal resistance and good biocompatibility.

Another refinement of the bushing according to one embodiment ischaracterized in that the holding element includes at least one flange,whereby the flange, for example, is electrically conductive. The purposeof the flange is to seal the electrical bushing with respect to ahousing of the implantable device. The holding element holds theelectrical bushing in the implantable device. In the variant of anembodiment described herein, the holding element includes at least oneflange on an external side. These flanges form a bearing, which can beengaged by the lids of the implantable medical device, for example,engaged in a tightly sealing manner. Accordingly, the holding elementincluding the flanges connected to it can have a U- or H-shapedcross-section. Integrating at least one flange into the holding elementensures that the electrical bushing is integrated into the implantabledevice in a safe, impact-resistant and durable manner.

The scope of one embodiment also includes an implantable medical device,for example, a cardiac pacemaker or defibrillator, having an electricalbushing according to at least one of the preceding claims. Features anddetails that were described in the context of the electrical bushingand/or the method shall obviously also apply in relation to theimplantable medical device.

Moreover, one embodiment also relates to a method for the manufacture ofan electrical bushing for an implantable medical device.

According to another aspect of one embodiment, a method for themanufacture of an electrical bushing for an implantable medical deviceis proposed,

whereby the method includes the following steps:

a) generating at least one base body green compact for at least one basebody from an insulating composition of materials;

b) forming at least one cermet-containing conducting element greencompact for at least one conducting element;

c) introducing the at least one conducting element green compact intothe base body green compact;

d) connecting the base body green compact to the at least one conductingelement green compact in order to obtain at least one base body havingat least one conducting element;

whereby the base body is connected to a holding element at a temperaturebetween 100° C. and 3,000° C.

The base body can be connected to the holding element, for example, bysimply contacting the two elements at the elevated temperature byheating the two bodies for several minutes, for example 10 to 1000, orhours, in one embodiment 0.2 to 50, in one embodiment 0.5 to 3, to ahigher temperature than room temperature. The temperature selectiondepends mainly on the selection of materials for the base body and theholding element. Accordingly, it is customary to select for a connectingprocess of this type, also called “diffusion bonding”, a temperaturethat corresponds to approx. 50-90% of the temperature of the highermelting material. This can be between 100° C. and 3,000° C., in oneembodiment between 500° C. and 2,700° C., in one embodiment between 700°C. and 2,500° C., for the materials according to one embodiment. It iscustomary to select the temperatures such that these are below thelowest melting material that is included in the method according to oneembodiment.

Usually, “diffusion bonding”, shall be understood to mean a process, inwhich two bodies made of different materials which are otherwisedifficult to connect are made to form a stable connection. For thispurpose, two different materials are contacted with each other atsuitable temperature and pressure conditions and kept at theseconditions for a certain period of time. At these temperatures andpressures acting on the connecting surfaces of the two materials, whichare usually elevated as compared to standard conditions, some masstransport proceeds between the two bodies that can establish a verystable connection between the two bodies.

The principle of “diffusion bonding” and the properties of the resultinglinks between two different materials are described in the publicationby Shizadi A. A. in Journal of Surface and Interface Analysis, vol. 31,no. 7 on pages 609-618, such that reference shall be made herewith tothe implementation of said process and the properties of the materialsthus processed.

In a further refinement according to one embodiment, the pressure actingon the base body and the holding element while the holding element isbeing connected to the base body is 0.2 to 20 MPa, in one embodiment ina range from 1 to 12 MPa. The pressure can be applied, for example, bymeans of a weight that is placed on the base body or the holdingelement. Moreover, it is preferred in one embodiment that the pressure,in one embodiment a starting pressure, during the connecting process isless than 1*10⁻⁴ mbar. Usually, the connecting process is carried out ina vacuum furnace.

In another refinement according to one embodiment, the holding elementconsists of a metal, at least in part. In one embodiment, the holdingelement is made from a material selected from the group consisting of ametal from any of the subgroups IV, V, VI, VIII, IX, and X of theperiodic system of the elements or at least two thereof. Moreover, in anembodiment according to one embodiment, the metal is selected from thegroup consisting of platinum, iridium, niobium, iron, molybdenum,tantalum, tungsten, titanium, cobalt, chromium, in one embodiment,cobalt-chromium alloys, and zirconium or two thereof.

Said metals can each be used alone or in combination with anothermaterial. Said other material can be the above-mentioned metals andalloys or further materials such as further metals. Alternatively or inaddition, alloys made from several of the above-mentioned metals can beused. Alternatively or in addition, mixtures or alloys made from one ormore of the above-mentioned metals and one or more further metals can beused just as well. These can be, for example, mixtures includingnon-metals such as metal oxides, such as ZrO, ZrO₂, Al₂O₃ and otherceramic materials.

In an embodiment according to one embodiment, the holding elementincludes niobium and the base body includes a zirconium oxide. Thezirconium oxide can be a zirconium(II) oxide (ZrO) or a zirconium(IV)oxide (ZrO₂) or a mixture thereof. In one embodiment, the base bodyincludes a zirconium(IV) oxide. Zirconium(IV) oxide is particularlyresistant to the action of acids and alkaline solutions which renders itparticularly well-suited for use in a medical device that may contactboth body fluids of various pH values and liquids and/or vapors andsubstances inside the device that also may be alkaline or acidic.Moreover, as a fired powder, ZrO₂ forms a particularly hard andresistant ceramic substance. The combination of ZrO₂ for the base bodyand niobium for the holding element has proven to be particularly stablewhen exposed to mechanical strain. The combination of ZrO₂-comprisingbase body and Nb-containing holding element allows a good connection by“diffusion bonding” to be attained.

In a refinement of the method according to one embodiment, the holdingelement includes a material selected from the group consisting ofniobium (Nb), platinum (Pt), iron (Fe), and molybdenum (Mo) or at leasttwo of these, and the base body includes an aluminum oxide. As a ceramicmaterial, aluminum oxide (Al₂O₃) features high mechanical resistance andis very well-suited for binding to metals such as Nb, Pt, Fe, Mo by“diffusion bonding”. In turn, said metals can be attached well to othercomponents, such as, for example, a housing of a medical device, bywelding, soldering or bonding.

It is preferable in one embodiment for the base body green compact to besubjected to firing together with the at least one conducting elementgreen compact.

In a refinement of the method, the base body green compact is subjectedto firing together with the at least one base body green compact. Saidprocess can, for example, be a sintering. Sintering can be used in oneembodiment for powder-like substances. This results in particularlytough, inert, and stable bodies being obtained, which, in addition, arebiocompatible in the majority of cases. Said bodies are particularlysuitable for use in implantable devices.

In another refinement according to one embodiment, step a) of thepreceding method described above includes a partial sintering of thebase body green compact.

In another refinement according to one embodiment, step b) of thepreceding method described above includes a partial sintering of theconducting element green compact.

Moreover, an electrical bushing is proposed that can be obtained havingthe method features of the embodiments of the method described above.

The scope of one embodiment also includes an implantable medical device,for example, cardiac pacemaker or defibrillator, having at least oneelectrical bushing according to at least one of the precedingembodiments.

The scope of one embodiment also includes the use of an electricalbushing according to any one of the embodiments of the electricalbushing for an implantable medical device described above.

The special feature of the method according to one embodiment resultsfrom both the base body and the conducting element comprising ceramiccomponents that can be processed in the scope of a sintering process. Inthe scope of step a), a base body green compact is generated from aninsulating composition of materials. This can be done by compressing thecomposition of materials in a mold. In this context, the insulatingcomposition of materials in one embodiment is a powder mass, in whichthe powder particles illustrate at least minimal cohesion. Usually, thisis effected in that a grain size of the powder particles does not exceed0.5 mm. In this context, the manufacture of the green compact proceedseither by compressing powder masses or by forming and subsequent drying.Said procedural steps are also utilized to form the cermet-containingconducting element green compact. In this context, one embodimentprovides the powder, which is compressed into the conducting elementgreen compact, to be cermet-containing or to consist of a cermet.Subsequently, the two green compacts—the base body green compact and theconducting element green compact—are combined. After this step, which iscalled step c), the two green compacts are connected, for example bysubjecting them to firing—which is also called sintering. Alternatively,other processes can be applied to connect the two elements, for examplegluing, soldering or welding of the elements.

In the firing process, the green compacts are subjected to a heattreatment below the melting temperature of the powder particles of thegreen compact. This leads to a substantial reduction of the porosity andvolume of the green compacts. The special feature of the method thus isthat the base body and the conducting element are sintered jointly.There is no longer a need to connect the two elements after this step.Through the firing process, the conducting element becomes connected tothe base body in a positive fit-type and/or non-positive fit-type and/orfirmly bonded manner. This achieves hermetic integration of theconducting element into the base body. There is no longer a need forsubsequent soldering or welding of the conducting element into the basebody. Rather, through the joint firing and the utilization of acermet-containing green compact, a hermetically sealing connectionbetween the base body and the conducting element is attained.

One refinement of the method according to one embodiment ischaracterized in that step a) includes a partial sintering of the basebody green compact, as has been mentioned above. The green compact ofthe base body is heat-treated in the scope of said partial sintering.This is already associated with some shrinkage of the volume of the basebody green compact. However, the volume of the green compact does notreach its final state. Rather, this requires another heat treatment inthe scope of step d), in which the base body green compact and theconducting element green compact are shrunk to their final size. In thescope of said variant of an embodiment, the green compact is heattreated only partly in order to already attain a certain surfacehardness to render the base body green compact easier to handle. This isexpedient for example, in the case of insulating compositions ofmaterials which can be compressed into a green compact shape only withsome difficulty.

Another variant of the embodiment is characterized in that theconducting element green compact is also already partly sintered in stepb). As described above for the base body green compact, the conductingelement green compact can also be partly sintered in order to alreadyattain a certain surface stability. It needs to be noted in this contextthat the final complete sintering occurs no earlier than in step d).Accordingly, the conducting element green compact attains its final sizeonly in step d).

FIG. 1 illustrates for exemplary purposes an implantable device 100,such as, for example, a cardiac pacemaker, that has an electricalbushing 10 integrated into its metallic housing. The electrical bushing10 is connected to the housing 110 of the implantable device 100 in ahermetically sealed manner, in one embodiment through welding. It istherefore advantageous in one embodiment that a holding element 20 ofthe electrical bushing 10 includes a metal that can be welded to thehousing 110 easily and reliably. The purpose of the electrical bushing10 is to establish an electrical connection between the hermeticallysealed interior of the medical device 100 and the exterior. Accordingly,a conducting coil 120, which is only indicated schematically here and isconnected to a stimulation electrode, can be connected to the electricalbushing 10. Stimulation electrodes of this type are inserted, forexample, in heart muscles to allow signals of the cardiac pacemaker tobe conducted to the muscle. In order to attain hermetic sealing, theconducting wire 30 is embedded in a base body 40. The base body 40 leadsto the formation of a hermetic seal between the holding element 20 andthe at least one conducting wire 30 in a through opening 22 formed bythe collar-like holding element 20. The electrically insulating basebody prevents electrical short-circuiting to occur between theelectrically conductive elongated conducting wire 30 and the metallichousing 110 and/or the metallic holding element 20.

In electrical bushings according to the prior art, a metallic wire isused as conducting element and needs to be soldered into a base body 40.For this purpose, the base body 40 includes a cylinder-like bushing forthe conducting element 30, with the internal wall of said bushing beingprovided with a metallic coating. The soldering has proven to beerror-prone and expensive. FIG. 2 illustrates an electrical bushing 10according to one embodiment that overcomes at least one of thedisadvantages mentioned above. The electrical bushing 10 includes acollar-like holding element 20. The holding element 20 serves to holdthe electrical bushing 10 in the implantable medical device 100. Theholding element 20, designed to be collar-like, includes athrough-opening 22. This is particularly evident from FIG. 3, whichillustrates a top view onto the electrical bushing 10 illustrated in asection in FIG. 2. Designed rectangular in shape and collar-like, theholding element 20 possesses, on its interior, the through-opening 22,which is designed to be rectangular in the present case. At least oneelongated conducting element 30 extends through said through-opening 22.In the exemplary embodiment illustrated, a total of five conductingelements 30 extend through the holding element 20. A base body 40 isarranged in the through-opening 22 in such a manner that hermeticsealing is effected between the holding element 20 and the conductingelement 30. The special feature according to one embodiment of theelectrical bushing 10 illustrated results from the conducting element 30comprising a cermet or consisting of a cermet.

A cermet is a composite material made of ceramic materials in a metallicmatrix. The special feature of a cermet-containing conducting element 50of this type is that it can be sintered jointly with the base body 40,which is also ceramic-containing, in a single procedural step. Thus, noundesirable through-openings, fissures or imperfections arise any longerbetween conducting element 50 and base body 40. Rather, a media-tightconnection is created between the two elements 40,50. The individualprocedural steps for the manufacture of the electrical bushing 10according to one embodiment are as follows:

a. generating a base body green compact for a base body (40) from aninsulating composition of materials;

b. forming at least one cermet-containing conducting element greencompact for a conducting element (30);

c. introducing the at least one conducting element green compact intothe base body green compact;

d. connecting the base body green compact to the at least one conductingelement green compact in order to obtain a base body (40) having atleast one conducting element (30).

The special feature according to the scope of the method according toone embodiment results from both the base body green compact and theconducting element green compact each being compressed from powders andthen subjected to firing. Accordingly, in just a few procedural steps agreen compact can be generated that includes both the conducting elementgreen compact and the base body green compact, and said total greencompact is then subjected to firing. In one variant of the embodiment,not only the base body 40 and the conducting element 30, but the holdingelement 20 also, are compressed from powders and sintered. Accordingly,the holding element 20 is also produced from a cermet-containing powderin one production step. Subsequently, the three green compacts—holdingelement 20, conducting element 30, base body 40—are joined. This resultsin the electrical bushing 10 in a green compact stage. Subsequently, thegreen compacts are jointly subjected to firing. The resulting electricalbushing 10 not only meets all necessary electrical requirements, but italso is produced in one step without any need for subsequent solderingor welding of individual elements. Moreover, the metal-containing, acermet containing holding element 20 enables a simple durable connectionto the housing of the implantable medical device 100 to be established.

FIG. 4 again illustrates a magnification of the individual components ofthe electrical bushing 10. This magnified detail corresponds to theregion denoted I in FIG. 3. Made from an electrically insulatingcomposition of materials, the base body 40 surrounds the conductingelement 30. Conducting coils, for example for a cardiac pacemaker, canbe connected to said conducting element 30. The base body 40 issurrounded by a holding element 20 that is designed to be collar-like inshape. Said holding element 20 is cermet-containing in the variant ofthe embodiment illustrated. Consequently, the holding element can besubjected to firing or sintering jointly with the cermet-containingbearing element 50 and the electrically insulating base body 40 in onestep. In one embodiment, the holding element 20 and the bearing element50 are made of the same material in this context.

For integration of the electrical bushing 10 into the implantablemedical device 100, the holding element 20 can include a flange. Aflange of this type has not been sketched-in in the figures. A housing110 of the device 100 can touch against the flange in order to enable ahermetically sealing connection of the two elements. In one embodiment,the holding element 20 and the flange are made of the same materialand/or as a single part.

FIG. 5 schematically illustrates the flow of a method for connecting theholding element 20 to the base body 40. In the first step 510, acomposite of a base body 40 and a conducting element 30 is generated, ashas been done above. Subsequently or concurrently, a holding element 20is manufactured by turning, milling or metal injection molding in asecond step 520. The holding element can be manufactured from a varietyof materials. In one embodiment, it is manufactured from a metal. Theholding element 20 can be selected, for example, from the groupconsisting of niobium (Nb), iron (Fe), titanium (Ti), platinum (Pt),iridium (Ir), molybdenum (Mo), tantalum (Ta), tungsten (W),cobalt-chromium alloys or zirconium (Zr) and two thereof. It is alsoconceivable to use an alloy made from any of the metals listed above andone of the other metals from the group or another metal. The holdingelement 20 is in one embodiment made from niobium or a niobium alloy.

The holding element 20 is joined to the composite of base body 40 andconducting element 30 in a third step 530 to form a bushing 10, as isillustrated in FIG. 9. In the process, one contact surface 970 of thebase body 40 each and one contact surface 980 of the holding element 20contact each other. The bushing 10 is placed on a base plate 910 of aheatable furnace 900 made by Degussa, Germany, in a fourth step 540, asis also illustrated in FIG. 9. In a fifth step 550, a weight 920 isapplied to the bushing 10. Said step 550 can be carried out eitherbefore or after step 540. The size and mass of the weight 920 depend onthe size of the bushing 10 and the contact pressure onto the boundarysurface between base body 40 and holding element 20 that is to beattained. In the example illustrated, the mass of the weight 920 wasapprox. 1,000 g. However, it is also conceivable to select the mass ofweight 920 to be higher or lower. In one embodiment, the mass is in arange between 100 and 5,000 g, in one embodiment, in a range between 500and 2,000 g.

The contact pressure exerted by weight 920 weighing 1,000 g depends onthe size and geometry of the bushing 10 and holding element 20. In theexample illustrated here, the external diameter 940 of the base body 40of the bushing 10 is approx. 3.5 mm and the internal diameter 950 of theholding element 20 is 2.6 mm. Due to the T-shaped geometry of thebushing 10 in this example, the bottom side 931 of the T crossbar of thebushing 10 is thus pressed onto the top side of the ring-shaped holdingelement 20 in order to form a joined connection 930. This generates aboundary surface of approx 4.3 mm² between base body 40 and holdingelement 20. The contact pressure in this case is approximately 2 MPa.Said pressure can be varied through suitable selection of the mass ofthe weight 920 or of the geometry of the contact surface of bushing 10and holding element 20. In one embodiment, the contact pressure in thiscontext is selected to be in a range from 0.5 to 10 MPa. The contactpressure is the sum of the pressure exerted by the weight onto thejoined connection 930 of base body 40 and holding element 20 and thenegative pressure existing in the furnace 900.

After placing the bushing 10 with holding element 20 and the weight 920into the furnace 900, a vacuum is applied to the furnace 900 in thesixth step 560 and the furnace 900 is heated to 1,700° C. for 2 hours.In this context, the temperature can either be constant or vary. In oneembodiment, the temperature in the furnace 900 is between 800 and 2,200°C., in one embodiment between 1,100 and 1,800° C., during the 1 to 4hour duration of the process. The pressure during the duration of theprocess is 0.2 to 20 MPa. The pressure can also be varied. In oneembodiment, the pressure in the furnace 900 is between 1 and 1 MPa.Moreover, it is preferred in one embodiment that a negative pressure, inone embodiment of less than 1*10⁻⁴ mbar, exists in the furnace 900during the connecting.

In order to attain a particularly durable and rapid connection to formbetween bushing 10 and holding element 20, the contact surfaces 970 ofthe bushing 10 and the contact surface 980 of the holding element 20 canbe processed in the first step 510 prior to the joining. Said processingcan, for example, involve polishing or grinding. Accordingly, it isadvantageous in one embodiment to select a roughness of the surfaces 970and 980 such that a mean roughness is less than 1 μm, in one embodimentless than 0.5 μm, in one embodiment less than 0.1 μm, and in oneembodiment less than 0.01 μm. By this means, the diffusion bondingprocess proceeding in the furnace 900, can be supported such that aconnection between bushing 10 and holding element 20 is durablyprovided, for example for several years, in one embodiment for severaldecades.

FIGS. 6 and 7 illustrate various geometries of bushing 10 and holdingelement 20. Accordingly, bushing 10 of FIG. 6 includes acermet-containing conducting element 30 that is surrounded by insulationmaterial, which forms a base body 40 around the conducting element 30.The bushing 10 formed in this example is rectangular in shape. However,any other shape, such as round, triangular shapes, are conceivable aswell such that the bushing can take the shape of a sphere or cube orcylinder or cone or any other three-dimensional shapes. In this context,the holding element 20 surrounds at least a part of at least oneexternal surface of the bushing 10. In this example, the holding element20 has an L-shaped cross-section such that the base body 40 can contactthe contact surface 980 of the holding element 20 through a contactsurface 970 on one of the internal surfaces of the L shape. A positivefit-type connection can thus be formed through said contact surfaces.The function of the holding element 20 in this context is to effect asimple connection to a housing of a medical device, into which thebushing 10 is to be introduced. This ensures that the housing of themedical device is hermetically sealed by the bushing 10 with the aid ofthe holding element 20. Since the holding element 20 is at least partlymade of metal, said connection to the housing can be effected, forexample, through soldering or welding. Alternatively, gluing processesare feasible just as well.

In FIG. 7, the cross-section of the bushing 10 has a T-shape. In thiscontext, a cermet-containing conducting element 30 is arranged in thestem of the T such that the conducting element 30 is surrounded on bothsides by an L-shaped insulation layer in the form of a base body 40. Ina three-dimensional view, the conducting element 30 is surrounded in aring-shape by the base body 40, whereby the diameter of the ringdecreases incrementally from one side of the conducting element 30 tothe other end. The purpose of the increment is to form a level contactsurface 970 on the base body 40 transverse to the orientation of theconducting element 30 within the base body 40 that enables contact to acontact surface 980 of the holding element 20. Due to the horizontalorientation of said contact surfaces 970 and 980, a weight 920, asillustrated in FIG. 9, can be used to facilitate a positive fit to formbetween bushing 10 and holding element 20.

FIG. 8 illustrates a bushing with holding element 20 and threeconducting elements 30 that are contacted through wires 55 and 60 andare incorporated into a housing 110 of a medical device that is notillustrated here. In this context, the internal wires 60 point to theinside of the device, whereas the external wires 55 enable thecontacting to an external device or a tissue. The wires 55, 60 areconnected to the cermet-containing conducting elements 30 through acontact surface 810.

FIG. 9 illustrates a furnace 900 that is filled by placing a bushing 10on its floor plate 910. The bushing 10 contacts a holding element 20 anda weight 920 on the furnace's bottom side 931 and top side 932,respectively. The weight 920 increases the pressure between the bushing10 and the holding element 20 under the bushing. As has been describedin FIG. 5, said furnace can be temperature-controlled and pressure canbe applied such that the elevated pressure acting on the joinedconnection 930 having the contact surfaces 970 and 980 enables fusion ofthe materials of the bushing 10 and holding element 20. In this example,the holding element 20 has an L-shaped cross-section. This not onlygenerates a large contact surface 980 to the bushing 10, but also twomore surfaces 981 and 982, for example as contact surfaces 990, 991, forcontacting a housing of a medical device (not illustrated here).

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A method for the manufacture of an electricalbushing for an implantable medical device, the method comprising: a.generating at least one base body green compact for at least one basebody from an insulating composition of materials; b. forming at leastone cermet-containing conducting element green compact for at least oneconducting element; c. introducing the at least one conducting elementgreen compact into the base body green compact; d. connecting the basebody green compact to the at least one conducting element green compactin order to obtain at least one base body having at least one conductingelement; wherein the base body is connected to a holding element, theholding element consisting at least in part of metal, via a diffusionbond formed at a temperature between 100° C. and 3,000° C., and whereina pressure acting on a connecting site between base body and holdingelement while the diffusion bond is formed between the holding elementand the base body, said pressure in a range from 0.2 to 20 MPa.
 2. Themethod according to claim 1, wherein the metal is selected from thegroup consisting of a metal from any of the subgroups IV, V, VI, VIII,IX, and X of the periodic system of the elements or at least twothereof.
 3. The method according to claim 2, wherein the metal isselected from the group consisting of platinum, iron, iridium, niobium,molybdenum, tantalum, tungsten, titanium, cobalt, chromium, andzirconium, or at least two thereof.
 4. The method according to claim 1,wherein the holding element includes niobium and wherein the base bodyincludes a zirconium oxide.
 5. The method according to claim 1, whereinthe holding element includes a material selected from the groupconsisting of niobium, platinum, iron, and molybdenum, or at least twothereof, and wherein the base body includes an aluminum oxide.
 6. Themethod according to claim 1, wherein the base body green compact issubjected to firing jointly with the at least one conducting elementgreen compact.
 7. The method according to claim 1, wherein step a)comprises a partial sintering of the base body green compact.
 8. Themethod according to claim 1, wherein step b) comprises a partialsintering of the conducting element green compact.
 9. A method for themanufacture of an electrical bushing for an implantable medical device,the method comprising: a. generating at least one base body greencompact for at least one base body from an insulating composition ofmaterials; b. forming at least one cermet-containing conducting elementgreen compact for at least one conducting element; c. introducing the atleast one conducting element green compact into the base body greencompact; d. connecting the base body green compact to the at least oneconducting element green compact in order to obtain at least one basebody having at least one conducting element; wherein the base body isconnected to a holding element via a diffusion bond formed at atemperature between 100° C. and 3,000° C.; and wherein either step a)comprises a partial sintering of the base body green compact or step b)comprises a partial sintering of the conducting element green compactsuch that one of the base body green compact and the conducting elementgreen compact is easier to handle.